With the rapid development of the power electronic technology, makes the application of the power electronic devices to be are used more and more widely. Wherein, the inverter is used widely in the application occasions power system, such as uninterruptible power supply (UPS), active power filter (APF), static var generator (SVG), and the like. In the art, various attempts and efforts have been made aiming at improving the respective specifications, such as decreasing the volume of the inverter, improving the efficiency of the inverter, reducing the cost of the inverter, decreasing eliminating the output harmonics of the inverter, the compatibility of three-phase-three-wire and three-phase-four-wire, and the like. However, various circuit topologies have their respective limitations, for example, the application condition of the respective prior circuit topology has its own respective limitations, and the respective problems cannot be solved excellently.
For example, some of the prior inverter topologies are shown mainly in FIG. 1 and FIG. 2. FIG. 1 shows a two-level inverter, and FIG. 2 shows a three-level inverter. In the prior art, IGBT having higher voltage must be selected for two-level inverter, while the efficiency and the switching frequency may be rather low. In order to reduce filter the switching ripple, larger filter must be designed, meantime, the loss is large. The three-level inverter can decrease the harmonic output and the volume to a certain extent, however, the harmonic output is still large, and deficiencies exist in the compatibility of the three-phase-three-wire and three-phase-four-wire.
In order to avoid the drawbacks which are mentioned above, a new design of inverter and its application system are the target desired to be accomplished by the industry.